In 1993, osteoporosis was identified as “one of the leading diseases of women” by Bernadine Healy, Md., then director of the National Institutes of Health. Complications following osteoporosis fractures are the fourth leading cause of death for women over the age of 65, following heart disease, cancer and stroke. It is the leading cause of disability in the United States and the most common cause of hip fracture.
Twenty-five million Americans suffer from osteoporosis, of which 85% are women. Type I osteoporosis, which is postmenopausal osteoporosis stemming from loss of estrogen, affects more than half of all women over 65 and has been detected in as many as 90 percent of women over age 75. Type II or senile osteoporosis which is strictly age related, affects both men and women usually over the age of seventy. Type III, the newest classification affecting both sexes, is drug-induced, for example, by long-term steroid therapy, known to accelerate bone loss. Patient groups that receive long term steroid therapy include asthmatics (7 million over the age of 18 in the United States) as well as patients with rheumatoid arthritis or other autoimmune diseases. Type IV is caused by an underlying disease such as rheumatoid arthritis (prevalence of 1-2% in the population).
Osteoporosis is responsible for a majority of the 1.5 million bone fractures each year leading to disabilities costing 10 billion dollars in medical, social and nursing-home costs. Even under the best care 40% of patients 65 years of age or older will not survive two years following a hip fracture.
In 1991, one in three American women were 50 years or older. The baby boom generation will begin to enter this age group in 1996. Because the average woman lives some thirty years after menopause, with present trends, osteoporosis threatens to be one of the biggest health threats of modern times.
Lifestyle can be a factor in onset of osteoporosis and in particular can be an important factor in building and maintaining healthy bone mass to prevent osteoporosis. Currently, persons under 65 are more likely than their parents to have had a sedentary lifestyle, bad eating habits, increased alcohol and caffeine intake, and a history of greater medication associated with bone loss. It is also clear that there is a genetic predisposition to the development of osteoporosis (see WO 94/03633 for a discussion of genetic factors in osteoporosis, which is herein incorporated by reference).
It would therefore be useful to be able to identify early those individuals at greatest risk for developing osteoporosis so that the individual can be counseled to make appropriate life style changes or institute other therapeutic interventions. For example, calcium supplements and exercise have been shown to be valuable preventive factors if used during a critical early age window. Hormone replacement therapy (HRT) has also been used successfully to combat osteoporosis occurring after menopause. HRT may be of greatest benefit if used early in the disease process before major bone loss has occurred. Since HRT has potentially serious side-effects, it would be useful for women to know their personal risk level for osteoporosis when making decisions about the use of HRT versus other interventions aimed at reducing the risk of developing osteoporosis.
The following published patent applications describe a variety of methods for diagnosing, monitoring and/or treating osteoporosis: WO 94/20615, WO 95/01995, WO 94/14844, EP93113604, WO/8809457, WO93/11149 and WO/9403633. The following references describe the association of various IL-1 gene polymorphisms in osteoporosis: U.S. Pat. No. 5,698,399; Eastell, R. et al., (1998) Bone 23 (5S): S375; Eastell, R. et al. and Keen, R W et al., (1998) Bone 23: 367-371.
Genetics of the IL-1 Gene Cluster
The IL-1 gene cluster is on the long arm of chromosome 2 (2q13) and contains at least the genes for IL-1α (IL-1A), IL-1β (IL-1B), and the IL-1 receptor antagonist (IL-1RN), within a region of 430 Kb (Nicklin, et al. (1994) Genomics, 19: 3824). The agonist molecules, IL-1α and IL-1β, have potent pro-inflammatory activity and are at the head of many inflammatory cascades. Their actions, often via the induction of other cytokines such as IL-6 and IL-8, lead to activation and recruitment of leukocytes into damaged tissue, local production of vasoactive agents, fever response in the brain and hepatic acute phase response. All three IL-1 molecules bind to type I and to type II IL-1 receptors, but only the type I receptor transduces a signal to the interior of the cell. In contrast, the type II receptor is shed from the cell membrane and acts as a decoy receptor. The receptor antagonist and the type II receptor, therefore, are both anti-inflammatory in their actions.
Inappropriate production of IL-1 plays a central role in the pathology of many autoimmune and inflammatory diseases, including rheumatoid arthritis, inflammatory bowel disorder, psoriasis, and the like. In addition, there are stable inter-individual differences in the rates of production of IL-1, and some of this variation may be accounted for by genetic differences at IL-1 gene loci. Thus, the IL-1 genes are reasonable candidates for determining part of the genetic susceptibility to inflammatory diseases, most of which have a multifactorial etiology with a polygenic component.
Certain alleles from the IL-1 gene cluster are known to be associated with particular disease states. For example, IL-1RN (VNTR) allele 2 (U.S. Pat. No. 5,698,399) and IL-1RN (VNTR) allele 1 (Keen R W et al., (1998) Bone 23:367-371) have been reported to be associated with osteoporosis. Further IL-1RN (VNTR) allele 2 has been reported to be associated with nephropathy in diabetes mellitus (Blakemore, et al. (1996) Hum. Genet 97(3): 369-74), alopecia areata (Cork, et al., (1995) J. Invest. Dermatol. 104(5 Supp.): 15S-16S; Cork et al. (1996) Dermatol Clin 14: 671-8), Graves disease (Blakemore, et al. (1995) J. Clin. Endocrinol. 80(1): 111-5), systemic lupus erythematosus (Blakemore, et al. (1994) Arthritis Rheum. 37: 1380-85), lichen sclerosis (Clay, et al. (1994) Hum. Genet. 94: 407-10), and ulcerative colitis (Mansfield, et al. (1994) Gastoenterol. 106(3): 63742)).
In addition, the IL-1A allele 2 from marker −889 and IL-1B (TaqI) allele 2 from marker +3954 have been found to be associated with periodontal disease (U.S. Pat. No. 5,686,246; Kornman and diGiovine (1998) Ann Periodont 3: 327-38; Hart and Kornman (1997) Periodontol 2000 14: 202-15; Newman (1997) Compend Contin Educ Dent 18: 8814; Kornman et al. (1997) J. Clin Periodontol 24: 72-77). The IL-1A allele 2 from marker −889 has also been found to be associated with juvenile chronic arthritis, particularly chronic iridocyclitis (McDowell, et al. (1995) Arthritis Rheum. 38: 221-28). The IL-1B (TaqI) allele 2 from marker +3954 of IL-1B has also been found to be associated with psoriasis and insulin dependent diabetes in DR3/4 patients (di Giovine, et al. (1995) Cytokine 7: 606; Pociot, et al. (1992) Eur J. Clin. Invest. 22: 396-402). Additionally, the IL-1RN (VNTR) allele 1 has been found to be associated with diabetic retinopathy (see U.S. Ser. No. 09/037,472, and PCT/GB97/02790). Furthermore allele 2 of IL-1RN (VNTR) has been found to be associated with ulcerative colitis in Caucasian populations from North America and Europe (Mansfield, J. et al., (1994) Gastroenterology 106: 637-42). Interestingly, this association is particularly strong within populations of ethnically related Ashkenazi Jews (PCT W097/25445).
Genotype Screening
Traditional methods for the screening of heritable diseases have depended on either the identification of abnormal gene products (e.g., sickle cell anemia) or an abnormal phenotype (e.g., mental retardation). These methods are of limited utility for heritable diseases with late onset and no easily identifiable phenotypes such as, for example, vascular disease. With the development of simple and inexpensive genetic screening methodology, it is now possible to identify polymorphisms that indicate a propensity to develop disease, even when the disease is of polygenic origin. The number of diseases that can be screened by molecular biological methods continues to grow with increased understanding of the genetic basis of multifactorial disorders.
Genetic screening (also called genotyping or molecular screening), can be broadly defined as testing to determine if a patient has mutations (alleles or polymorphisms) that either cause a disease state or are “linked” to the mutation causing a disease state. Linkage refers to the phenomenon the DNA sequences which are close together in the genome have a tendency to be inherited together. Two sequences may be linked because of some selective advantage of co-inheritance. More typically, however, two polymorphic sequences are co-inherited because of the relative infrequency with which meiotic recombination events occur within the region between the two polymorphisms. The co-inherited polymorphic alleles are said to be in linkage disequilibrium with one another because, in a given human population, they tend to either both occur together or else not occur at all in any particular member of the population. Indeed, where multiple polymorphisms in a given chromosomal region are found to be in linkage disequilibrium with one another, they define a quasi-stable genetic “haplotype.” In contrast, recombination events occurring between two polymorphic loci cause them to become separated onto distinct homologous chromosomes. If meiotic recombination between two physically linked polymorphisms occurs frequently enough, the two polymorphisms will appear to segregate independently and are said to be in linkage equilibrium.
While the frequency of meiotic recombination between two markers is generally proportional to the physical distance between them on the chromosome, the occurrence of “hot spots” as well as regions of repressed chromosomal recombination can result in discrepancies between the physical and recombinational distance between two markers. Thus, in certain chromosomal regions, multiple polymorphic loci spanning a broad chromosomal domain may be in linkage disequilibrium with one another, and thereby define a broad-spanning genetic haplotype. Furthermore, where a disease-causing mutation is found within or in linkage with this haplotype, one or more polymorphic alleles of the haplotype can be used as a diagnostic or prognostic indicator of the likelihood of developing the disease. This association between otherwise benign polymorphisms and a disease-causing polymorphism occurs if the disease mutation arose in the recent past, so that sufficient time has not elapsed for equilibrium to be achieved through recombination events. Therefore identification of a human haplotype which spans or is linked to a disease-causing mutational change, serves as a predictive measure of an individual's likelihood of having inherited that disease-causing mutation. Importantly, such prognostic or diagnostic procedures can be utilized without necessitating the identification and isolation of the actual disease-causing lesion. This is significant because the precise determination of the molecular defect involved in a disease process can be difficult and laborious, especially in the case of multifactorial diseases such as inflammatory disorders.
Indeed, the statistical correlation between an inflammatory disorder and an IL-1 polymorphism does not necessarily indicate that the polymorphism directly causes the disorder. Rather the correlated polymorphism may be a benign allelic variant which is linked to (i.e. in linkage disequilibrium with) a disorder-causing mutation which has occurred in the recent human evolutionary past, so that sufficient time has not elapsed for equilibrium to be achieved through recombination events in the intervening chromosomal segment. Thus, for the purposes of diagnostic and prognostic assays for a particular disease, detection of a polymorphic allele associated with that disease can be utilized without consideration of whether the polymorphism is directly involved in the etiology of the disease. Furthermore, where a given benign polymorphic locus is in linkage disequilibrium with an apparent disease-causing polymorphic locus, still other polymorphic loci which are in linkage disequilibrium with the benign polymorphic locus are also likely to be in linkage disequilibrium with the disease-causing polymorphic locus. Thus these other polymorphic loci will also be prognostic or diagnostic of the likelihood of having inherited the disease-causing polymorphic locus. Indeed, a broad-spanning human haplotype (describing the typical pattern of co-inheritance of alleles of a set of linked polymorphic markers) can be targeted for diagnostic purposes once an association has been drawn between a particular disease or condition and a corresponding human haplotype. Thus, the determination of an individual's likelihood for developing a particular disease of condition can be made by characterizing one or more disease-associated polymorphic alleles (or even one or more disease-associated haplotypes) without necessarily determining or characterizing the causative genetic variation.